Servo system and control thereof



April 5, 1949.

J. A. PEOPLES, JR., ET AL SERVO SYSTEM AND CONTROL THEREOF 6 Sheets-Sheet 1 Filed March 30, 1943 9 m Q m w w m A HE. E d

EVA H ETAL 2,466,041

6 Sheets-Sheet 3 Ap 5, 1949. J. A. PEOPLES, JR.,

I SERVO SYSTEM AND CONTROL THEREOF Filed March 30, 194:5

April 5, 1949. J. A. PEOPLES, JR., ERAL 2,466,041

SERVO SYSTEM AND CONTROL THEREOF Filed March 30, 1945 6 Sheets-Sheet 4 RATE April 5, 1949. J. A. PEOPLES, JR., ETAL 2,466,041

SERVO SYSTEM AND CONTROL THEREOF Filed March 50, 1943 6 Sheets-Sheet. 5

FIG. l4

FIG. l5

Ap 5, 1949. J. A. PEOPLES JR, EI'AL SERVO SYSTEM AND CONTROL THEREOF 6 Shee tsSheet 6 Filed March 30, 1943 FIG. I6

SIGNAL TRANS.

Patented Apr. ;1949

James A.

. Raymond C.

I Delaware Peoples, Jr., Richard Scheib, Jr., and

Goertz, Hempstead, N. Y., assignors-to The Sperry Corporation,

a corporation of Application March so, 1943, Serial No. 431,172 ,1'9 Claims. (01. 121-41) Our invention particularly relates to hydraulic servo systems and also to control elements and combinations thereof which are responsive to hydraulic conditions or pressures in the system for providing extremely accurate, quickly responsive and stable operations of the system. In the following, we have described our novel systems and control elements therefor as embodying a -Vickers" type transmission mainly for exemplary purposes. A transmission of this character comprises an A end including pistons driven by a motor, and lever means for varying the displacement of these pistons, whereby the flow of oil, or other liquid which may be employed, through a connecting, circulating system to the 3 end, is controlled both in direction and rate. The B end comprises a hydraulic motor, driven by the fluid supplied from the A end, which serves to move or position a positionable element such, for example, as a gun turret. The rate of operation of the B end and its direction will depend upon the control over the A'end. A piston, herein called a stroke regulating piston, which is connected to the control lever of the A end of. the transmission system, functions in response to the liquid supplied to the cylinder thereof to position the control lever of the A end of the Vickers transmission, regulating thedisplacement of the pistons therein and thereby controlling the output speed of the B end.

' It will be understood that the novel valve of our invention, hereinafter particularly described, may be employed to control any fluid-actuated element such as a power piston and it has particular application in controlling the stroke regulating piston of a hydraulic servo system. In the following, when we refer to a stroke regulating piston, we mean the piston which is employed to controlthe A end of a Vickers type hydraulic transmission or servo system, movement of the stroke regulating piston causing changes in the displacement of the A end' and thereby changes in the output speed'of the 3" end.

Since our invention particularly resides in control elements and combinations thereof which are admirably suited to control the stroke regulating piston of a transmission system of the foregoing character, we have illustrated and in the following described the various control elements and combinations in connection with a stroke regulating piston and a Vickers system controlled thereby. However, it will be understood that the various novel control elements and combinations thereof may be employed and may fulfill the same function in other types of systems.

The first object of our invention resides in providing a valve for controlling the admission of fluid under pressure to a cylinder having a piston therein, or to any work-performing device, and

the exhaust of fluid therefrom, which valve is so' constructed and arranged that the rate of the piston, or other element driven by the fluid, will be substantially proportional to the force which is applied to and efiects an operation of said valve.

Another. object resides in providing a valve adapted to fulfill the above function but which,

due to the novel construction, thereof, requires no mechanical connection between the valve element and the power piston or stroke regulating piston con rolled thereby or the provision 'of additional m ans for returning a signal-responsive torque motor and the valve element connected therewith to neutral or null position. It 15 a further object to provide a novel control valve of the foregoing character which provides a piston-rate to applied force proportionality which is substan-- tially a constant and which is somewhat independent of fluid or liquid viscosity. More particularly, it is an object ofour invention to provide a control valve having the foregoing operationalcharacteristics which will, due to the novel construction thereof, return to a neutral or cut-off position when the applied displacing force has been relieved.

It is another object of our invention to provide a control valve of the character above pointeed out for controlling the displacement of an element or piston. b fluid means which control valve includes means for effecting a rate of displacement of said element or piston which is substantially' linearly proportional to the control force applied to said valve.

' Another object lies in'the provision of a hydraulic system including a valve of the above character and repeat-back means whereby acceleration of the driving end of the hydraulic transmission is approximately proportional to the force applied to the valve.

Other objects lie in providing a system of this character in which a manually operable speed control lever lies in a neutral position for all uniform speeds; and one in which the position of the manual control or the force applied to it wil. provide an indication of the operational speed of the hydraulic transmission. v Other objects reside in providing in a hydraulic system a valve of the character hereinbefore pointed out together with means, cooperable therewith to provide a wipe-out of the speed lag, which occurs under transient conditions, when a steady state or uniform speed-output condition prevails.

Still a. further object resides in providing in -a hydraulic system means for obtaining a'hydraulic signal which is proportional to the torque and torque rate of a force applied, for example, by a signal-responsive element to the valve; and, more particularly, wherein the hydraulic torque Q accompanying drawings, in whichvalves shown in Figs. 1' and of Fig. 8;

and torque rate signal is obtained through a delayed-repeat-back action to the element applying the valve-displacing force.

our, invention will best be understood from the following description read in connection with the Fig. 1 is a somewhat schematic sectional view showing one form of the control valve of our invention associated with a piston;

Fig. 2 is a longitudinal section through a valve of the form disclosed in Fig. 1, but slightly modified;

Fig. 3 is a transverse section of Fig. 2 taken in about the plane 3-3 thereof;

Fig. t is an elevation view, partially in section,

showing a preferred construction of the valve piston;

Fig. 5-is a somewhat schematic representation.

of a modified form oi valve;

Fig. 6 is a longitudinal section through a valve similar to that disclosed in Fig. 5, but slightly Fig. 7 schematically discloses a .servo system embodying a valve operable in the manner of the Fig. 8 is a schematic representation of a manually operable, speed control system in which the control valve of our invention is employed;

Fig. 9 discloses a modification of the system Fig. 10 illustrates a characteristic curve of the valve controls of Figs. 1 or5;

11 is a somewhat schematic view of a modificat on of the valve of Fig. 1;

Fig. 12 is a somewhat schematic showing of a modification of the valve of Fig. 5;

Fig. 13 discloses a servo system embodying the valve of our invention and means for providing a speed lag with wipe-out repeat-back thereto;

Fig. 14 is a view, partially in section, of a control valve and associated piston together with the lands 8 slidably fit within the enlarged bores 4 and I. An inlet passage l0, whichis adapted to be connected with a source of fluid or a liquid under pressure, communicates through an inlet port with the zone 3 of the valve casing; and exhaust passages II and "communicate, respectively, with the enlarged portions of the zones of the bores I and 5 and between adjacentlands 8 and 8. The inlet passage in communicates with the bore of the valve between the lands 8, and a second pair or intermediate passages I3 communicat through ports with the bore of the valve. The passages 13 serve to connect the valve I with the cylinder it within which the work piston controlled thereby or the stroke regulating piston i5 is slidably fitted. It will be understood, of course, that in hydraulic servo systems the piston rod I8 of the stroke regulating piston is-connected with the control lever of the A" end of the Vickers" transmission. One of the passages l3 communicates with the cylinder 14 on one side of th piston I! while the other communica'tes therewith but to the other side of the piston. Thel piston valve 6 is adapted to be slid axially of t e valve casing to control both the admission of fluid under pressure to one side of the piston l5 and the exhaust of fluid from the other side thereof. In the neutral position of the valve piston, that is, when no fluid is supplied to the cylinder I, the lands 8 are designed in registry with the ports of the passages owever, when the valve piston is moved in one direction or the other, for example, to the right'as viewed in Fig. 1, fluid under pressure,

to l1 l3.

which is supplied to thebcre of the valve and between the lands 8, will enter on passage l3 through the intermediate port and cause the piston ii to move toward the left. However, simultaneously. when the piston valve is moved in the above manner, the other land 8 will open the other intermediate'port and permit fluid to exhaust means for providing a speed lag with wipe-out control of an associated servo system;

Fig. 15 is a view, partially in section, of a unit for supplying a hydraulic actuating pressure to .the valve of our invention, which hydraulic presstrolseregulating piston of a Vickers" type transmission, I indicates generally th valve casing which, however, is preferably formed as shown in Fig. 2. Fig. 1 serves to illustrate, for the purposes of general explanation, the construction of the valve shown more specifically in Figs. 2, -3

and 4. The casing i is provided with a longi--;

tudinal bore indicated generally at 2 which includes the zone 3 of a diameter smaller than that of the zones 4 and 5. Preferably, the zone 3 of lesser diameter, lies intermediate the zones 4 and 5 of greater but preferably equal diameters.

Within the bore 2 is slidably fitted a piston valve 6 build up a pressure between the lands 8 and 8 Since, the area of the land 9, which is'subjected to this from the cylinder into the bore of the valve and between the lands 8 and 8.

In accordance with our invention, the exhaust passages ii and i2 are provided with a restricting orifice Ila and 1211, respectively, which are designed to retard the flow ofexhausting fluid therethrough and cause a fluid pressure -to be built upbetween adjacent lands 8 and 9. Therefore, when the piston valve is movedtoward the right as above explained, exhausting fluid will at the left-hand end of the piston valve.

fiuidpressure, is greater than that of land 8, a resultant pressure occurs tending to, move the piston valve toward the leftv in opposition to the movement thereof which initiated the build-up of pressure in the exhausting liquid and a movement of the stroke regulating piston.

The rate of flow of the exhausting fluid which is'retardedby the restricting orifices Ila or I211 is determined by the rate of the stroke regulating piston i 5. Flu'thermore, .the rate of fluid flow will be independent of any'load on the piston. Therefore, the pressure built up in the exhausting fluid is a function of piston rate and since the pressure developed by the exhausting fluid exerts a. proportional force urging the piston value in a direction opposite to that in which it moved to initiate movement of the piston l5,the rateof movement of the piston liwill be approximately comprising a stem 1 and pairs of spaced lands 8 and 9. The lands 8 are .adapted slidably to fit within the zone 3. of the valve casing while proportional to the force applied to the piston valve, In other words, it may be said that the force applied to the piston valve by the exhaust fiuidws proportional to the rate of movement of the piston l3.

Although the pressure build-up in the exhaust,- 'ing fluid is a function of piston rate, the relationship therebetween depends upon the nature of the orifice and fluid viscosity. However, by employing a thin edged orifice, the pressure to rate of flow relation will be practically independent of viscosity thereby substantially eliminating the effect of changes in fiuid temperature on this relation.

The control valve for the stroke regulating piston is preferably made in the form shown in Figs. 2'and 3, wherein a sleeve is rotatably intiarposed between the valve casing and the valve piston. ,As shown in Fig. 2, the valve casing i1 is provided with a longitudinal bore l8- of substantially uniform diameter throughout. A sleeve I9 is rotatably fitted within the bore I8 and is provided with zones of lesser and greater internal diameters corresponding to the zones 3, 4 and 5 of the schematic showing in Fig. 1. valve 6, comprising the pairs of lands 8 and 9, is slidably fitted within the sleeve l9, and the lands 8 control the flow of fluid through ports which communicate with circumferential grooves 2| on the exterior of the sleeve. Grooves 2| preferably register with circumferential grooves 22 formed in the walls of the bore l8. The grooves 22'communicate through ports with the intermediate passages I3 and with the cylinder of the stroke regulating piston as above described. The walls of the bore l8 are also provided with circumferential grooves 23 which register with ports 24 extending laterally through the sleeve l9 and also communicate through ports with exhaust passages and I2 which include restricting orifices (not shown) as above described. Likewise, the inlet passage H1 in the valve casing communicates with registering annular grooves 25a and 25b in the valve casing and sleeve, groove 25b in the sleeve communicating with the bore within the sleeve through ports 25. Relative longitudinal movement of the sleeve with respect to the valve casing may be prevented by providing the sleeve with an exterior, circumferential groove within which the split ring 26 may be received and secured to the valve casing. One end of the sleeve l9 has mounted thereon and secured thereto a gear 2'! which is adapted to mesh with a gear 28 on the shaft 29 of a motor (not shown). With this construction, the motor mayserve continuously to rotate the sleeve i9 of the valve, whereby substantially to eliminate static friction between the valve piston and the sleeve. However, the valve piston may be operated to control the flow of fluid to and the exhaust of fluid from the cylinder of the stroke regulating piston in the manner hereinabove described.

In Fig. 4, We have illustrated a preferred manner of constructing and assembling the piston valve. The stem 1 of the piston and lands 8 are formed as an integral unit, and both ends of the stem 1 are provided with integral enlarged cylindrical ends 30 having shoulders 3|. An annular element 32 is adapted to fit around the enlarged ends 30, but the interior diameter thereof is slightly greater than the diameter of the enlargement 30. At one end of the piston, a washer 33 is adapted to prevent movement of the ring 32 axially of the piston valve but to allow eccentric or lateral movement thereof whereby, if the zones 3, 4 and 5 of the valve or the valve sleeve vary slightly in eccentricity, the valve piston may be properly fitted therewithin. A stud The piston 34 serves to complete the assembly forming the land 8 at one end of the valve piston. At the other end thereof, a ring 35 similar to that above described is-mounted over the enlargement 34, and a washer 36 servesto hold it against axial movement. A nut 31 is threaded on the end of the piston stem securely to hold the washer 38 and assembly in place while an end member 38 to which an operating rod or wire 38 is connected may be fastened to nut 38 by the screws 48. This construction allows for slight misalignnients of the zones of the valve with which the lands of the valve piston cooperate in controlling fiow of fluid therethrough while assembly thereof is relatively simple.

In Fig. 5;we have shown a modified form of valve which functions in substantially the same manner as that hereinabove described to provide a rate of movement of the stroke-regulating piston which is proportional to the force applied to the piston of the valve. In the somewhat schematic showing of this modification, we have illustrated generally a valve casing at 4| within cludes a stem 45 having lands 46 which may be formed integrally therewith. In the embodiment illustrated, the valve piston includes three lands, the central one of which is adapted to register with an inlet port through which an inlet passage 41 communicates with the bore of the valve. The inlet passage, of course, will in operation connect with a suitable source of fluid under pressure, and a movement of the valve piston in either direction will control the flow of this fluid to one or the other of the intermediate passages 48 which also communicate with the .bore of the valve. end lands are so arranged relative to the central bore andthe enlarged ends 43 thereofthat when the piston valve is moved in one direction or the other sufiicient to permit fiuid under pressure to pass to one of the intermediate passages 48, one of these lands will permit the exhausting fluid to flow intothe adjacent enlarged zone 43 of thebore and thence to the exhaust passage as or 50. M

In practice, as shown in Figs. 5 and 6, the bore or sleeve is preferably of suflicient length to provide adequate bearing surfaces for the end lands. the bore or sleeve being grooved or slotted respectively, adjacent the end lands an axial distance sufficient to exhaust the fiuid from one intermediate passage when the piston is moved to admitfiuid under pressure to the other inter- Furthermore, it is not necessary to provide enlarged end zones in the bore of the valves shown in Fig. 5 but the grooves or slots above described may be employed to pass exhaust fluid from one side of the end lands to the other side thereof as shown in Fig. 6.

Each of the exhaust passages has a restricting, preferably thin-edged, orifice 5| associated therewith whereby to cause the exhausting fluid to develop a pressure in the enlarged zone of the valve bore to which it is admitted. Since the fluid pressure so developed will exert a force on the outer side of the end land while the fluid pressure against the other side thereof and one side of the intermediate land will bef'equal, a

resultant force will be produced tending to move the valve piston back to a neutral position or to a The positionjin which the intermediate land covers the Q inlet poi-t.

Since in this modification of our valve we employ the action of fluid under pressure against the ends of the piston valve, the ends of the bore are closed, as shown, and the valve-operating member or wire which connects the valve piston with some suitable torque motor extends through a small orifice 53 formed in one of the end walls of the Valve casing. In order to simulate substantially the same conditions at the other end of the valve casing, the closure member for the bore at that end may also be provided with a small orifice, as shown. Furthermore, these orifices may be used to cause the exhausting fluid to develop a pressure against the outer sides of the end lands sothat orifices may be omitted.

In Fig. 6 we have shown a preferred construction of the valve schematically shown-in Fig. 5, wherein a rotatably mounted sleeve is interposed between the valve casing and the valve piston for the same purpose as the sleeve l8 hereinbefore described in connection with Fig. 2. In the embodimnt shown thevalve casing 54 includes exhaust passages 49 and 58, intermediate passages 48, and an inlet passage which communicates with .the interior bore of the sleeve as hereinafter described. The casing 54 has a longitudinal bore 55 therein of substantially uniform diameter throughout, and the sleeve 56 which is rotatably fitted therewithin also has an interior bore of substantially uniform diameter. The exhaust passages 49 and 50 communicate with circumferential grooves 51, respectively; with which ports 58,

extending laterally through the sleeve 58, are adapted continuously to register. The intermediate passages 48 also communicate with circumferential grooves 59 in the walls of the bore of the valve casing with which lateral ports 50 in the valve sleeve continuously register. The inlet the motor 1:. Actuation of the valve piston o. in one direction or the other is effected by means 'oi' the torque motor 14.

motor may be employed in connection with the valves of ourinvention, but it will be. observed that no centralizing springs or other means are required to returnthe armature thereof to aneutral or null position afterthe signal has faded or gone to zero. .For exemplary purposes, the torque motor comprises the core 14a on each leg of which are mounted coils I5 and I6, respectively. The armature "thereof is connected to the wire or rod 52 extending from the piston valve 5.

The electrical control circuit which controls the operation of the torque motor preferablyincludes a phase sensitive amplifier-demodulator and a "Selsyn transmitter 18 and synchro-receiver-l8 connected as shown. The Selsyn transmitteris connected to a suitable source of alternating current, and when the rotor thereof-reflects an angular displacement of some control or reference element, a'signal will be supplied to the torque.

motor to effect an operation of the servo system to move the positionable element in the same irection as the reference member and through the same angular displacement. The position repeat-ha k is obtained through synchro-receiver I 19, which is connected to the Selsyn transmitter in any standard manner so as to provide anA. C;

. output voltage from the'receiver which is propassage communicates through a port-6| with the through a small orifice in an end plate 54 which is preferably secured to the sleeve in any desired mannerand serves to prevent axial movement of the sleeve in one direction relative to the valve casing. A gear 85 is fastened to the other end of the sleeve 56 to impart rotary movement thereto and in conjunction with the shim 66 prevents relative axial movement between the sleeve and the valve casing.

In Fig. 7, we have disclosed for exemplary purposes and in a somewhatschematic manner one form of servo system and controls therefor inportional to the error and which reverses in phase when passing from a lagging error to aleadin'g error. For illustration purposes, we have shown the rotor of the synchro-receiver connected with the transmission through shaft and-gear 8| which meshes with gear 69. The synchro-receiver is connected through transformers 82 and 83 with the parallel branch circuits of a phase sensitive amplifier which in the embodiment shown pro- I vides full wave demodulation. The secondaries of the transformers 82 and 83 are connected,

respectively through conductors 84 'and 85 with twin triode tubes 86 and 81. The plates of the. tube 86 are connected across the secondary of the transformer, the primary of which is connected to a source of alternating current 208, to

which the Selsyn transmitter is also connected.

Likewise, the plates oi tube .81 are connected across the secondary of a transformer. 88a, the primary of which is also connected to the source 208 of alternating current.

A mid-tap on the secondary of transformer-88 is connected through conductor 89 to the coil 15 of the torque motor and, in a similar manner, a mid-tap from the secondary of transformer 88a is connected.

through conductor 90 .to the coil 15 of-the torque motor. The opposite ends of each of the coils i5 and 16 are connected together and through conductor SI, and resistor 92 t0 the cathodes of the two tubes. 'Mid-taps on the secondaries of eluding a valve for controlling the stroke 'egulating piston which may comprise either of the forms hereinabove described. In this system the Vickers transmission, including both the A and B ends thereof, is represented generally at 81, the stroking piston generally at 58, and the output of the transmission is represented as gear 69 meshing with gear 18 and driving the load shaft H to which the positionable member is connected. Our novel valve indicated generally at 12 includes the piston valve 8 of the characterhereinbefore described and the sleeve l8 which is rotated by transformers 82 and 83 are connected together through a resistance 83 and frbm a central tap on said resistance through resistor 92 to the cathodes of the two tubes. In order to obtain a rate repeat-back from the output of the servo system, we may mount a voltage generator 94 on the output shaft thereof and connect it through conductors 95 and 96- across the resistor 93, a condenser 91 being included in one of the legs thereof.

It will be understood that the. foregoing de-.

scribed-system is represented in the main for.

the purpose of describing the operation of a system including our novel control valve. Assuming Any form of torque I proportional to .the displacement of a reference member, this signal will be'transmitted through i that the Selsyn transmitter provides a signal I the phase sensitive amplifier to one of the coils of the stroke-regulating piston at a rate proportional to the force applied to the piston valve 6 from. the torque motor and will cause the transmission system to rotate the load shaft in one direction or the other depending on the phase sense of the signal and at a speed which is dependent upon the position which the piston 68 assumes. The repeat-back of the movement of the positionable member occurs through the synchro-receiver, and when 'both the reference member and the positionable member have experienced a displacement of like magnitude, the signal will be reduced to zero.

Furthermore, the repeat-back from generator 94 to the phase sensitive amplifier will reduce the signal to zero when the .positionable member is being moved'in timed relation to the reference member, and under this condition the piston valve 6, due to the pressure reaction thereon, will return to a cut-ofl position. The generator 94 impresses a voltage across the resistance 93 and capacitance 91 which is proportional to the rate or speed of the transmission output. ,By making the time constant of the series condenser and resistor network sumciently large, it is possible to obtain stable operation without objectionable speed lag.

It will be observed that in a servo system employing a valve of the character herein described that the valve piston itself serves to restore the armature of the torque motor to its original position, thereby eliminating any need for springs or other devices for returning it to null position, which devices are ordinarily not highly dependable but vary in characteristic with wear and usage.

Figs. 8 and 9 disclose novel speed control servo. systems employing our novel form of valve. In Fig. 8, the valve I2 is shown connected to control the stroke-regulating piston 68 of a Vickers type transmission, the piston rod thereof being connected with the control lever 98 'for the A" end of the transmission. A manual control lever 99 is adapted to impart a force to the piston 6 of the control valve 12. In the embodiment illustrated, this is accomplished through an intermediate lever I09 to which lever 99 is connected, preferably, intermediate the ends thereof through link 99a. One end of lever I00 is connected through spring IOI to the piston vave 6 of the valve, and the other end thereof is pijl'rotally connected at I02 to one end of a piston rod I03. Rod I03 is provided with piston I04 which is slidably fitted within cylinder I05 and biased by springs I06 to a central position. A fluid circulating system comprising the conduits I01 and I08 is connected with the cylinder I05 on opposite sides of the piston therein'and to a fluid-pump I09. Pump I09 is of a [reversible type and driven from the B end.of the Vickers transmission. A bypass conduit 0 having an orifice III therein is connected between the two branches of the circulating system and between the pump I09 and the cylinder I05. In this system, the manual control lever 99 is' designed to occupy a position which is indicative of the speed of operation of the transmission system. For this purpose, therefore, a dash-pot I I2 is provided, and the lever 99 is connected to the piston therein through a spring I I3. In practice,'sprlng l I3-is stronger than the spring IM and, likewise, springs I05 are relatively strong springs, that is, spring II3 ofiers greater resistance to compression or tensile forces, than spring IOI.

In operation, the lever 99 is moved to apply a force to the piston valve 9 of the control valve in one direction or the other. This causes the stroke-regulating piston 68 to move at a rate proportional to the force applied on the control lever 99 and to accelerate the servo system. Assuming, that the lever 99 is forced downwardly, having a fulcrum at its point of connection with spring II3, the system is arranged to cause the pump I09 associated with the B end of the transmission to build up a pressure through conduit I08 to the lower end of cylinder I05. The rate at which the pump I09 pumps fluid is determined by the B end speed and since the fluid passes through orifice I I I, the fluid pressure developed by the pump is proportional to the B end speed. As the pressure develops in the cylinder, it will force piston I04 upwardly, the position thereof being determined by the B end speed, thereby progressively relieving the pressure applied on the piston 6 of the control valve through the operation of the manual control lever 99. The motions of piston I04 and control .lever 99 are added differentially, and when the' B end speed is sufiicient to produce a pressure in the cylinder I05 which will entirely wipe out the applied force to the piston valve 6, the control valve will cut ofi the supply of fluid to the stroke-regulating piston, and the system will therefore continue to operate at this speed while the manual control lever 99 will remain in the position to which it was moved in initially applying the force to the valve 6, the action of the dash-pot connected thereto providing this operation.

Alternatively, the fiuid pressure developed by pump I09 could be applied directly to the piston of control valve I2. In this event, it would be necessary to maintain the control forceon the piston 6 and the dash-pot would be eliminated.

As above explained in connection with the operation of the system shown in Fig. 8, the position of the manually controlled lever 99 is indicative of the rate of the output of the servo.

'It will be noted that when a displacing force is transmitted to the piston valve 6 of the control applied to lever 99, a corresponding force is valve with a resulting displacement of said piston valve from a neutral position thereby producing an acceleration of the servo output. By means of the hydraulic repeat-back signal which operates.

the piston I04 and its associated piston rod, the force applied to the control valve is wiped out by a displacement of the piston rod I03 which corresponds to the speed'of the output of the servo. When these conditions obtain, the output rate of the servo is a constant. The wipeout of the signal applied to the control valve occurs without any substantial'movement of the control lever 99, and since the displacement produced by the repeat-back signal is a measure of the position of the lever arm will be a measure of f the output rate of the servo; When, of .course, the force displacing the piston valve 6 from its neutral or unactuated position ls reduced to zero, the restoring pressure developed by the exhausting fluid will restore the piston valve to its initial,

neutral position.

In Fig. 9 we have illustrated only aportion of a servo system, the balance of which may be generally similar to that-shown in Fig. 8. Both of these systems are manually operable, speed control arrangements.- In the control arrangement of Fig. 9, however, the manually operated lever 99 will assume a neutral-position for all uniform speeds of operation of the transmission system. In this control system, it is to be understood that the .valve I2 is connected to the cylinder of the" stroke regulating piston 58, and the cylinder I is connected in the fiuid circulating system and to the conduits I01 and I08 as above described in connection with Fig. '8. Therefore, the control of the Vickers transmiss'ionand the repeat, back to the cylinder I05 is substantially the same.

as above described. In this embodiment, however, the lever 99 is connected between centering springs H4, andispivotally supported at fulcrum 99b whereby it may be moved in opposite directions to actuate lever II5 through link 99a. One end of lever H5 is connected With'the piston 6 of the control valve I2 through the spring IOI while the other end thereof is connected to adash-pot Ill. The piston of the dash-pot is connected to the piston rod I03 and the cylinder thereof is connected at II8 to the lever II5'as shown. A centering spring H6 is also connected to the lever II5 and dash-pot II! at H8 for-centering the cylinder of the dash-pot.

In the operation of this form of control, let

us assume that lever 99 is urged in a downward direction, thereby imparting a force to the piston 6 of the control valve I2 which in turn causes the B end of the transmission to accelerate. This downward movement of lever arm 99 will cause lever II5 to pivot upwardly about its connection with the cylinder of dash-pot I I1. When the speed of the- B end of the transmission, through. the medium of the pump I09, develops sufllcient pressure in the lower end of cylinder I05 as to move dash-pot I I1 upwardly, this movement will cause lever II 5 to rotate about its connection with the link 99a and thereby wipe out the force applied to the piston 6-} The valve piston will therefore return to. cut-01f position and the system will'continue to operate at the speed'developing the pressure which was sufficient to wipe out .the original signal. When the force is relieved on the piston'G, the-manually operated lever 99 will return to its original position through the action of the centering springs II4.

Centering springs Il4and H6, in practice, ofler greater'resistance to compression or tensile forces than spring Illl. v The operation of the system fragmentarily shown in Fig. 9 is, as hereinabove indicated, generally the same as that shown in Fig. 8 with the exception that the manually operated lever arm 99 returnsto a neutral position when released Y and therefore will occupy a neutral position for- .all constant output rates of the servo. In the system of Fig. 9, it will be observed that a displacement force is appliedto the piston valve 6 of the control valve which is dependent upon .the

amount of displacement of the control lever 99 r from a neutral position. The hydraulic repeatback signal which actuates the piston I04 and its associated piston rod I03 is, of course, proportional to the output rate of the servo and the resulting displacement of lever II5 through the dash-pot I II will be suflicient to reduce the pressure applied to the control valve to zero. The reduction of the manually applied displacing force on the piston valve to zero by the hydraulic repeat-back signal is accomplished without materially affecting the lever 99 and, therefore,

when a condition of constant speed output of theservo is reached and the lever arm 99, is re-,- leased, arm 99 will return to a neutral position under the influence of centering springs II4. When, of course. the rate signal repeat-back reduces the displacing force on the piston valve to zero, the restoring pressure developed by the exhausting fluid will restore the piston valve to its neutral position blocking the admission of fluid under pressure to and the'exhaustof fluid from the passages I3. the output rate of the servo is a constant.

The valves disclosed in Figs. 1 and 5 provide,

' as hereinbefore' explained, ,a rate of the strokeregulating piston which is proportional to'the.

force applied to the piston of the controlvalv'e. However, as indicated in Fig. 10, the curve representing the rate-to-force proportion over a desirable range of forces is not linear but generally will assume the configuration represented at H9. It is desirable, however, that the rate control valve have an operating characteristic represented by the linear curve I20. To approximate a performance curve of the latter character, we

prefer to arrange our valves in the manners disclosed in Figs. 11 and 12.

The valve shown in Fig.\l1 conforms in all essential-details to the valve of Fig. 1 but, in this form of our invention, a secondary orifice I2I is provided in the exhaust passage. The orifice I2'I provides an outlet for fluid from the passage I22 which communicates with the bore of the valve casing and between said bore and the primary orifice Ila. In accordance withour invention a 7 piston I 23 is slidably fitted within the passage I22 and serves to control the size opening of the -may be enlarged as shown, and a compression secondary orifice 'I2I. The end of the piston I 23 sprin I24 may be interposed between-it and a threaded plug I25 forming a closure for the end 'of the passage Within which the enlarged end of the piston slides. A suitable vent is provided, of course, to discharge fluid which may leak past the piston I23.

When but a comparatively smallforce. is applied to the piston valve 5 of the control valve,

the orifice II a is adequate to provide a rate-to-' force relationship which is substantially linear. However, for higher forces the exhausting fluid pressure develops to'a greater magnitude than it should to preserve the linearrelationship, and the biasing spring I24 associated with the control piston of the secondary orifice I2! is so arranged as to permit the exhausting fluid pressure to move the piston I23 and thereby to open the secondary orifice I2I to a degree proportional to the exhausting fluid pressure. With this arrangement, a more linear relationship of rate-to-for'ce is attained. As shown, this construction is car- 'ried out both with the exhaust passage II and the exhaust passage I2. Likewise, as shown in Fig. 12, a similar arrangement of elements is Under such conditions,

provided'in order for the control valve to be endowed with the desired performance character- .istics.

In Fig. 13, we have shown a servo system which is controlled in a modified manner, and the details of operation of this particular type of control will be explained in connection with Fig. 14. Referring first to Fig. 14, we have disclosed a combination of elements for providing a speed lag with wipe-out, hydraulic control of the control piston valve 5 of the stroke regulating valve. The stroke regulating valve is of the type shown in Fig. 1, including the exhaust passages II and i2 and exhaust orifices Ila and I2a. Orifices IIb and I21) preferably larger than the asso ciated orifices I la or I Ib may be included in the exhaust passages II and I2, respectively, and between the orifices IIa or I21: and the bore of the valve body for damping purposes. In accordance with this modification of our invention, volumetrically displaceable means are connected with the exhaust passages of the control valve and communicate therewith between the bore of the valve body and the exhaust orifices II a and I2a, respectively, or, in each case between the orifices Ha and III) or IM and I2b. In the embodiment shown, we have used Sylphon bellows I25 and I27, the interiors of which lie in communication with the exhaust passages II and I2, respectively. Compression of these bellows is preferably accomplished by the compression springs I28.

When the piston valve 6 of the control valve is moved in one direction, for example, to the right, fluid under pressure is admitted to the right side of the piston I5 and fluid passes to the exhaust passage II, and since the rate of fiow of fluid through orifice I Ia is small, most of this exhaust fiuid will act to expand bellows I26. If orifice I Ia were completely closed, the back ressure and therefore the reaction force on the valve would be proportional to the displacement of piston I5. This gives the system the speed lag characteristic necessary for stability. The orifice Ila allows this volume of fluid to slowly leak out after a new speed has been established, providing a speed lag wipe-out system.

In Fig. 13, we have shown the above-described modified valve connected in a servo system. This system may in all general respects conform to that disclosed in Fig. '7. However, it will be noted that due to the operation of the bellows providing both a speed lag and signal wipe-out repeatback, this system need not include any electrical rate circuit,-but this function is supplied in a hydraulic manner.

In Fig. 15, we have disclosed a combination of elements which will provide a hydraulic pressure to actuatethe piston of the control valve which is proportional both to torque and to time rate of change of torque applied thereto by the signal responsive torque motor. The torque motor may be of the general character illustrated in Fig. 7 and comprising the armature i1, core 740,, and energizing coils I5 and '75. The body I29 of this device which may be indicated generally at I30 has passages I3I and I32 formed therein which are adapted to be connected, respectively, to the spaces within the bore of a valve of the character shown in Fig. 1 and between the end lands 9 and the ends of the bores which are closed, as illustrated in Fig. 16. At. the lower ends thereof, these passages communicate through ports with enlarged zones I33 and I34, respectively, these zones being provided with outlets I35 which 14 may communicate with the sump of the system. fPistons I35are associated with thearmature 11 of the torque motor and serve to control the rate of fiow of fluid from the passages I3I and I32, respectively, to the sump. Fluid under pressure is supplied continuously to these passages through an inlet passage I31 and branch passages I38 and I39, in each of which is interposed a restricting, preferably thin edged, orifice I40. In the embodiment herein illustrated, passages I31 and I38, I39, in part, are formed in a block I29a, inserts provided with the orifice I40 being secured therein, and the block then being secured within the body I29 as shown. Suitable gaskets may be used to prevent leakage from the passages I'38 and I35 between the body and block.

Normally, when no signal is applied to the torque motor l4, fiuid under pressure will flow from the inlet passage I3'I- to both passages I3I and I32 and to the zones of the bore of the control valve cylinder which lie on opposite sides of the piston valve 6 therein. Furthermore, fluid will exhaust from the passages I3I and I32 through the exhaust openings I35 at substantially equal rates so that equal fluid pressures will be supplied to both ends of the piston valve 6., However, when the armature of the torque motor, in response to a signal, is actuated in one direction or the other, for example in a clockwise direction, the piston I35 will move toward the port at the end of passage I3I, thereby restricting theexhaust of fluid therefrom and developing a high pressure in this passage which will be communicated to the valve. Also, the other piston I36 will move away from the associated port end of the passage I32, reducing the pressure in passage I32 which is communicated to the other side of the piston valve as shown in Fig. 16, The result will be a force which tends to move the piston valve in one direction or another.

A second passage I i: communicates through an orifice I412 with the passage I3I and, similarly, a passage M3 communicates through an orifice I M with the passage I32. These orifices are preferably thin edged orifices. The passage MI is substantially closed at one end by a piston I47 slidably fitted therein and associated with armature II. This piston transmits the force exerted thereon by the fluid in passage MI to the armature I? of the torque motor. At the other end thereof, passage MI communicates with an enlarged bore M8 having a piston I49 slidably fitted therein. A compression spring I50 is interposed between piston I 49 and a plug I 5| which closes one end of the enlarged bore. A vent I45 is preferably provided to exhaust fluid which may leak past piston I49. The foregoing construction is carried out in association with thepassage I43, that is, a piston I52 is associated with the armature 'I! of the torque motor and disposed in pressure responsive relation to fluid within the passage I43. An enlarged bore I55 at the other end of passage I43, provided with a piston I56, compression spring I51 and plug I58, substantially duplicates the construction hereinbefore described.

The pressure difierential which will be built up in passages I3I and I32 for a given torque developed by the torque motor will depend upon the net reaction of pistons I36, I41 and I52. Therefore, for a given applied torque, the pressure differential in I 3| and I32 will be greater if this pressure diiferential is not transmitted to passages Ill and I43. The spring loaded pistons communicating with each of these passages make it necesl sary for oil'to flow through orifices I42 and I44 before a change in pressure in -I4I and I43 can occur. The motion of pistons I41 and I52 is at all times so small as to have small effect on-the volume occupied by the oil. It therefore follows that if a torque is suddenly developed by the torque motor the pressure differential in I3 I and I32 will be large at first and then decrease as the change in pressure is transmitted to pistons I41 and I52. It also follows the pressure signal which is transmitted to the piston valve associated therewith depends not only upon the torque developed by the motor, but also upon the time rate of change of the torque. The output may then be said to nearly be proportional to the input plus a term proportional to the rate of change of the input. The relative amounts of these two functions depend upon the dimensions of the system, i. e., the effective areas and lever arms of the pistons I36, I47 and I52, and by the time constant of the pressure response of passages MI and I43. This is controlled by the size of the orifices I42 and I44 and by the spring constants of I50 and I5! and by the areas of pistons I49 and I56. The part of the signal which is proportional to the rate of change of applied torque tends to make the system more stable.

The operation of the embodiment of our invention shown in Fig. 15 is as follows and it will be "noted that the corresponding embodiment shown in Fig." 16 will function in substantially the same manner. When no signal is applied to the torque motor I4, the armature 'I'I thereof will occupy the zero signal position shown in Fig. 15. However, when a signal is supplied to the torque motor, the armature thereof will be displaced either in. a clockwise or counter-clockwise direction and through an angle dependent upon the magnitude of the signal ,voltage. Assuming that the armature is displaced in a clockwise direction, the fluid pressures in the passages I3I, I32 will be differentially varied due to the change in. position of the pistons I36. Under the assumed clockwise rotation, the pressure in passage I3I will increase while that inyI32 will decrease. Because of the restricting orifice I42, fluid flowing from the passage I3I to the passage Iti will be time delayed' However, after a time interval, the fluid pressure in passage I4I will equal that in I3I assuming no greater signal is supplied increasing the angle of displacement of the armature 11 from its zero signal position. The'fluid pressure in passage MI is, of course, applied to the piston I47 which operates to apply a restoring force urging the armature toward its zero signal position. The cross-sectional area of the piston I41 which is exposed to the fluid .under tons I41 or I52, due to movement thereof with the armature in eifecting the initial displace ment, is substantially eliminated. When, however, the pressure builds up in. either passage I or I43, after a time interval determined by the dition will provide a differential fiuid pressure in passages I3I and I32 which is proportional to the displacement of the armature or to the magnitude'of the control signal voltage. The initial pressure differential, under the above assumed signal build up, due to the initial dispressure in the passage I4I and the distance of the piston I4I from the pivotal axis of the armature 'I'I are so chosen that this restoring force is insuflicient to return the armature to its zero signal position, but will partially restore the armature to this position. Of course, the conve e will occur if the armature were to be moved in a counter-clockwise direction from its. zero signal position by virtue of thepiston I52.

It will be noted that displacement of the armature from its zero signal position in response to, let us assume, a signal building up to a constant magnitude is opposed by the fluid pressure reaction on the pistons I36. Initially,- this' is substantially the only pressure reaction affecting the armature because the pistons I49 and I56 may move to compress the springs associated therewith and therefore pressure reaction on the pisplacement of the armature will be substantially proportional to the signal voltage supplied to the torque motor plus the rate of change thereof.

It is believed that the foregoing description of the operation of the embodiment of our invention shown in Fig. 15 will show that the differential fluid pressures produced thereby constitute hydraulic signals which in magnitude are proportional both to displacement and rate of displacement of the input thereto. In other words, the differential hydraulic signals appearing in passages I3I and I32 are substantially proportional to the displacement of the armature of the associated torque motor and to the rate of change of displacement of said armature. These hydraulic signals are adapted to be transmitted from the passages I3I and I32 through suitable connections (not shown) to a control valve of the character of those herein shown and illustrated. Fig. 16 serves clearly to illustrate how these differential hydraulic pressure signals are applied to one embodiment of the control valve of the present invention wherein the force applied in displacing the valve from its neutral position is derived from fluid applied differentially to both ends of the piston valve. Obviously, hydraulic pressure could be applied in a similar manner to operate the piston valve of any of the embodiments of our control valve herein shown and described through, for example, suitable bellows, pistons or the like which are operatively subjected to said differential fiuid pressure and which are connected with the piston valve of the valve to apply a force thereto and to move the same in accordance with such differential fluid pressure signals.

The hydraulic system disclosed in Fig. l6 includes a device of the character hereinabove described in connection with Fig. 15 with the ex ception that, instead of employing an expansion chamber or cylinder fitted with a spring biased piston, a Sylphon bellows is substituted therefor. However, fluid under pressure is supplied through conduit I 59 and conduits I60, each including a restricting orifice I6I, to two conduits I62 and I63, which schematically represent the passages I3I and I32 in Fig. 15, and to the bore in the casing of the control valve 12 between the end lands of the piston valve 6 thereof and the closed ends of the bore indicated generally at I 64, respectively. Conduits I65 and I66 conform to passages MI and I43 of Fig. 15, and orifices I61 and I68 conform to the orifices I42 and I44, respectively. 'Spring compressed bellows I69 and I16 are substituted for the enlarged bores and associated pistons I48, I49 and I55, I56.

When a signal is applied to the torque motor, the armature 11 thereof causes a sudden high pressure to develop either in the conduit I62 or the piston valve 6 of the stroke rate'valve 12 in one direction or the other. Through the operation of the orifices I61 and I 68 and associated bellows, operablein response to the fluid pressure therein, the force applied to the piston valve 8 will be proportional to the torque and torque rate of the armature 11. This hydraulic signal will therefore cause the transmission I1I comprising the A end driven by a suitable motor M2, to drive the 8" end thereof in accordance with this signal. The original signal, of course, may be derived from the Selsyn transmitter H3 and through the synchronous transformer 61% and amplifier-demodulator I15 which is phase sensitive. A positional repeat-back to the transformer may be derived from the B end. of the transmission and through shaft I16 and meshing gears i16a in substantially the same manner as described in connection with Fig. '7.

However, in this system, we have additionally provided for a hydraulic rate repeat-back. To accomplish this, a conduit I11 is connected to conduit E19 of the fluid circulating system repwhich will produce an added reaction to the resented by the conduits I18 and I19'between the A and B ends of the transmission. A piston we is schematically represented as slidably positioned in one end of the conduit I11 and has an enlarged end I8I suitably fitted within a cylinder I82. A compression spring I83 is interposed between the enlarged piston end I8! and the opposite end of the cylinder. Conduit I84 is connected with one end of the cylinder I82, and the other end thereof, as schematically shown, has a piston I85 slidably fitted therein and associated with the armature 11 to impart a force thereto which is dependent upon the pressure in the .conduit I84. Fluid is supplied to this conduit through a conduit I86 and a restricting orifice I81, and fluid is exhausted from this conduit through an orifice I88 which may be comparatively larger than the orifice I81.

Likewise, a similar cylinder I82 and its associated parts are associated with a conduit I89 which connects with the conduit I18 of the fluid circulating system between the A and B ends of the transmission system. Further, the cylinder I82.is connected with a conduit I94 which is adapted to supply fluid pressure to a piston I95 associated with the other end of the armature 11 of the torque motor. Fluid is supplied from v the conduit I88 to the conduit I94 through restrict ng orifice I90 and is exhausted therefrom through conduit I96 in which an. orifice I91 is included. Orifices I81 and I98 are so correlated in size opening with respect toorifices I88 and I91 as to maintain the conduits I84 and I94 preferably filled with fluid or oil. The conduits I84 and I94 and associated parts are adapted to transmit a torque to the armature 11 of the the system is changed.

The lastdescribed portion of our system is de-' torque motor when the pressure in the conduits I18 and I19 between the A and "3 ends of signed to provide a hydraulic repeat-back to the drive its load shaft and an appreciable load is suddenly applied thereto, a relatively brief, in-

stantaneous pressure differential will be created in the branches of the last-described portion of our system comprising the' conduits I84 and I84 armature of the torque motor to cause the Piston of the control valve to be operated in a direction either to increase or decrease the A end output of the transmission depending upon the speed of response and stability characteristics'of' the system and thereby provide a faster responding or more stable system. 1

Due to the differential areas of the pistons I98 at one end thereof and the enlarged end I8! thereof, a relatively high hydraulic pressure will not be delivered through the pistons I or I 95 to the torque motor armature but pressures of relatively low magnitude but proportional to the pressures in the fluid circulating conduits I18 and I19. Therefore, these latter pressure reacthe control pistonwhich is substantially pro-' portional to torque and torque rate of the armature of the torque motor'or, in other words, to displacement and rate of change of displacement of the control or error. It will be noted that the 'Sylphon. bellows I69 and I18 and their associated springs function in connection with the hydraulic circuit associated therewith, which is the equivalent of that shown in Fig. 15, to provide a signal proportional to torque and torque rate in substantially the same manner as hereinbefore described. However, in Fig. 16 we have addltionallyshown a further means for hydraulically controlling the system to compensate for changes in load. This latter signal is in addition to the primary. control signals proportional to displacement or torque and torquerate and does not affect the servo or the control over the servo. system other than as hereinabove described to compensate for load changes and the like.

It will, of course, be understood that further pressure reactions or differential pressure reactions may be derived from various portions of a servo system and applied to the torque motor in substantially the same or a manner similar to that hereinbefore described in connection with the system comprising conduits I84 and I94.

It will be understood that we prefer to employ oil as the working medium in our servo systems. Furthermore, it will be understood, although we have. not illustrated the return connections, that provision is made to return the fluid discharged through the various orifices to the sump of the system.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from .the'scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

19 -What is claimed is: v

1. A valve for controlling fluid flow to an element movable thereby comprising a valve body provided with a longitudinal bore having zones of; unequal transverse area, an inlet passage, an exhaust passage, and a second pair of passages communicating through ports with said longitudinal bore in axially spaced relation, said sec-- and pair of passages being adapted to convey fluid to and from opposite sides of said element,

' a piston valve having spaced lands slidably fitted within said zones of the longitudinal bore, afirst provided with a longitudinal bore therein, a bis-' ton valve having spaced lands slidably fitted therewithin, said body having an inlet passage,

1 an exhaust passage and a pair of passages all terminating in ports'communicating with said longitudinal bore, said pair oi passages being ,adapted to connect with opposite sides oi said element, said valve piston being provided with pair of lands of lesser transverse area being arranged cooperatively with said ports to control the flaw of fluid under pressure from said inlet passage to one of said second pair of passages and the exhaust oi fluid from the other of said second pair of passages to said exhaust passage, the portoi said exhaust passage lying between adjacent lands of lesser and greater area, and means for causing the exhausting fluid to develop a pressure in. the space between said adjacent lands.

2. A valve for controlling fluid flow to an element movable thereby comprising a valve body provided with a longitudinal bore having zones of unequal transverse area, an inlet passage, an. exhaust passage, and a second pair of passages communicating through ports with said longitudinal bore in axiallyspaced relation, said sec-' ond pair of passages being adapted to convey fluid to and from opposite sides of said element, a piston valve having spaced lands slidably fitted within said zones of the longitudinal bore, a, first sure in the space between said adjacent lands.

3. A valve for controlling fluid flow to an element movablethereby comprising a valve-body provided with a longitudinal bore of a lesser diameter in'an intermediate zone and of a greater diameter adjacent both ends of said intermediate zone, an inlet passage communicating through an inlet port with said intermediate zone, a first pair of passages adapted to convey fluid to and from opposite sides of said element and communicating through ports with said intermediate zone and on opposite sides of said inlet port and a pair of exhaust passages communicating through exhaust ports with said bore and on opposite sides respectively of the ports of said pairoi passages, a piston valve having spaced lands, two thereof being slidably fitted within the intermediate zone of said bore to control the flow of fluid from said inlet passage to one of said first pair of passages and simultaneously to control the flow of fluid from the other of said first pair of passages to one of said exhaust passages, and one land being slidably fitted within each end zone of said bore and spaced from adjacent lands with an exhaust port therebetween, and means associated with the exhaust means operable when said piston is moved in one direction to place the inlet and one of said pair of passages in communication and the other of said pair of passages and th exhaust port in communication, means forming a variable-orifice for causing the exhausting fluid to develop a fluid pressure, means responsive to the fluid pressure so developed for varying the size of said orifice, and means subjected to said exhausting fluid for urging said valve piston in the opposite direction. 1

- 5. A valve for controlling fluid flow to an element movable thereby comprising a valve body provided with a longitudinal bore therein,-a piston valve having spaced lands slidably fltted therewithih, said body having an inlet passage, an exhaust' passage and a pair of passages'all terminating in ports communicating with said longitudinal bore, said pair oi! passages being adapted to connect with opposite sides of said element, said valve piston being provided with means operable when said piston is moved in one direction to connect the inlet with one of said pair of passages and to connect the other of said pair of passages withthe exhaust passage, means forming a first oriflce oifixed size opening for causing the exhausting fluid to develop a fluid pressure and means forming a second, variable orifice'associate'd with said exhaust passage and providing parallel paths for the exhaust of said fluid, means responsive to the fluid pressure so developed i'or 'varying the size of said second orifice, and means subjected to said exhaustingfluid for urging said direction.

6. A valve for controlling fluid flow to an element movable thereby comprising a valve body provided with a longitudinal'bore having zones of unequal transverse area and an inlet passage, an exhaust passage and a pair of passages communicating through ports with said longitudinal bore in axially spaced relation, said pair of passages being adapted to connect with opposite valve piston in the opposite sides of said element, a piston valve having spaced lands slidably fitted within said zones of the longitudinal bore, a first pair of lands of lesser transverse area being arranged cooperatively with said ports to control, when said piston is moved in one direction, the flow oi fluid under pressure from said inlet passage to one oi said pair of passages and the exhaust oi fluid from the. other of said pair of passages to said exhaust passage, the ports of saidexhaust passage lying between adjacent lands of lesser and.

greater. area, means forming a flrst orifice of fixed size opening for causing the exhausting fluid to develop a fluid pressure and means forming a second, variable oriflce associated with said exhaust passage and providing parallel'paths for the exhaust'of said fluid, means responsive to the fluid pressure so developed for varying the size of said second orifice, and means subjected to said exhausting fluid for urging said valve piston in the opposite direction. a

' 7. In a valve for controlling fluid flow to an element movable thereby, a valve body provided. with a longitudinal bore therein, a sleeve ro-- tatably mounted within said bore, said sleeve having zones of unequal transverse area and being provided with a plurality of lateral ports therein, said valve body being provided with an inlet passage, an exhaust passage and a pair of I exhaust passage, the port of said exhaust passage lying between adjacent lands of lesser and greater area, means for causing'the exhausting fluid to develop a pressure in the space between said adjacent lands, and means for imparting rotary movementv to said sleeve.

8. In a valve for controlling fluid flow to an element movable thereby, a valve body provided with a longitudinal bore therein, an inlet and exhaust passage and a pair of passages communicating through ports with said bore, piston means slidably fitted within said bore and provided with means for closing the ports to said pair of passages when said piston means lies in neutral or unactuated position but operable, when said piston means is moved, to pass fluid from the inlet port to one of the pair of passages and from the other of said pair of passages to the exhaust passage, said piston means and said valve body being so constructed, correlated and arranged as to expose a surface of sufficient magnitude of said piston means to exhausting fluid when said piston means is moved from its initial position under an applied force in one direction as to urge itin the opposite direction, means forming an orifice associated with the exhaust passage for causing said exhausting fluid to develop a pressure, and volumetrically variable means associated with said exhaust passage between said orifice and bore for providing a delayed restoring, fluid pressure signal acting on said piston means and substantially proportional to the rate of said applied force with an elimination of said signal when said piston means is restored to its neutral or unactuated position. J

9. In a valve for controlling fluid flow toan element movable thereby, a valve body provided with a longitudinal bore therein, an inlet and exhaust passage and a pair of passages communicating through ports with said bore, said pair of passages being adapted to be connected to opposite sides of said element, piston means slidably fitted within said bore and provided with means for closing the ports to said pair of passages when said piston means lies'in neutral or unactuated position but operable, when said piston means is moved, to pass fluid from the inlet port to one of the pair of passages and from the other of said pair of passages to the exhaust passage, said piston means and said valve body being so constructed, correlated and arranged as to expose a surface of'sufficient magnitude of said piston means to exhausting fluid when said piston means is moved in one direction as to urge it in the opposite direction, means forming an orifice associated with the exhaust passage for causing said exhausting fluid to develop a pressure, volumetrically variable means communicating with the space between said orificeand the bore of said valve body and adapted to expand under a relatively high exhaust fluid pressure, and means for compressing said variable means whereby to provide a delayed pressure reaction.

10. In a valve for controlling fluid flow toanelement movable thereby, a valve body provided with a longitudinal bore therein, an inlet and exhaust passage and a pair of passages communicating through ports with said bore, said pair of passages being adapted to be connected to opposite sides of said element, piston means slidably fitted within said bore and provided with means for closing the ports tosaid pair of passages when said piston means lies in neutral or,

unactuated position but operable, when said piston means is moved, to pass fluid from the inlet port to one of the pair of passages and from the otherof said pair of passages to the exhaust passage, said piston means and said valve body being so constructed, correlated and arranged as to expose a surface of suflicient magnitude of said piston means to exhausting fluid when said piston means is moved in one direction as to urge it in the opposite direction, means forming an orifice associated with the exhaust passage for causing said exhausting fluid to develop a pressure, and expansible means comprising a bellows communicating with the space between said orifice and the bore of said valve body and resilient means for compressing said bellows.

11. In a servo system, the combination with a valve for controlling fluid flow to an element movable thereby and comprising a valve body provided-Winnie longitudinal bore therein, an

, inlet, exhaust and a pair of passages communieating through p'orts'with said bore, piston means slidably fitted within said bore and provided with means operable, ',.when said piston means is moved, to pass fluid from the inlet port to one of said pair of passages and from the other of said pair of passages to the exhaust .port, said piston means and said valve body being so constructed, correlated and arranged as to expose a surface of suflicient magnitude of said piston means to exhausting fluid when said piston means is moved in one direction as to urge it in the opposite direction, of means including signal responsive means for producing a fluid presstore thesignal-responsive means to its zero si .nal position.

12. In a servo system, the combination with a valve including movable means operable when mot ed in one direction to control a fluid flow to an element movable thereby and the exhaust of fluid therefrom, said valve including means responsive to exhausting fluid pressure for urging said movable means in the opposite direction and means for causing the exhausting fluid to develop a pressure, of signal-responsive means, means controlled by said signal-responsive means .for actuating said fluid control means in accordance with displacement of said signal-responsive means from its zero signal position, means controlled by said signal-responsive means including time delay means for producing a delayed restoring force and means for applying said restoring force to said signal-responsive means, the restoring force being of such magnitude and the applying means being so correlated and arranged with respect to said signal-respon-i sive means as to only partially restore the signalresponsive means to its zero signal position.

'13. In a servo system, the combination with a valve including movable meansoperable when moved in one direction to control a fluid flow to an element movable thereby and the exhaust of fluid therefrom, said valve including means responsive to exhausting fluid pressure for urging said movable means in the opposite direction and means for causing the exhausting fluid to develop a pressure, of means for applying fluid pressure to actuate the fluid control means of said valve and signal-responsive means for controlling the last mentioned fluid pressure, means responsive to said last mentioned fluid pressure including time delay means for producing a delayed restoring force, and means for applying said force to said signal-responsive means, the restoring force being of such magnitude and the applying means being so correlated and arranged with respect to said signal-responsive means as to only' partially restore the signal-responsive means to its zero signal position.

i 14. In a servo system, the combination with a valve including movable means operable when moved in one direction to control a fluid flow to an element movable thereby and the exhaust of fluid therefrom, said valve including means responsive to exhausting fluid pressure for urging means responsive to the exhaust fluid pressure forvarying the size of said orifice, and means subjected to said exhaust fluid for operating said valve means.

17. In a system for controlling the operation of a fluid driven motor means and including means for supplying fluid under pressure to said motor and means for exhausting. fluid therefrom, the-combination with valve means for controlling the admission to and exhaust of fluid from said motor means, of means forming a first orifice for causing the exhausting fluid. to develop a fluid pressure, means forming a variable orifice metrically variable means communicating with said last mentioned fluid pressure, means actuated by fluid pressure in said volumetrically variable means for applying a restoring force to said signal-responsive means, and means for delaying.

the build-up of pressure in said volumetrically variable means.

15. In a servo system, the combination with a valve including movable means for controlling the flow of fluid to and the exhaust of fluid from an element movable thereby, of means for applying fluid pressure to actuate said valve, signalresponsive means for controlling said fluid pressure in accordance with displacement of said signal-responsive means from its zero-signal position, and means responsive to the controlled fluid pressure including time delay means for producing a delayed restoring force and means for applying said force to said signal-responsive means, the restoring force being of such magnitude and the applying means being so correlated and arranged with respect to said signal-responsive means as to only partially restore the signalresponsive means to its zero signal position.

16; In a system for controlling the operation of a fluid .driven motor means and including means for supplying fluid under pressure to said motor and means for exhausting fluid therefrom, the combination with valve means for controlling the admission to. and exhaust of fluid from said motor means, of means forming a variable orifice associated with said exhaust means for causing the exhaust fluid to develop a fluid pressure.

associated'with said exhaust means for causing the exhausting fluid to develop a fluid pressure, means responsive to the exhaust fluid pressure for varying the size of said variable orifice, and means subjected to the exhaust fluid pressure produced by said oriflces for operating said valve.

18. The combination recited in claim 16 in which the valve means includes means defining ports connected in the system and a piston valve cooperable with said ports and movable from a neutral position to cause an operation of the motor' means, and the exhaust fluid is applied to said piston valve in a manner to restore it to its neutral osition.

19. The Eombination recited in'claim 17 in which the valve means includes means defining ports connected in the system and a piston valve cooperable with said ports and movable from a neutral position to cause an operation of the motormeans, and the exhaust fluid is applied to said piston valve in a manner to restore it to its neutral position.

" JAMES A. PEOPLES, JR. RICHARD SCHEIB, JR. -RAYMONDC. GOERTZ.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 901,613 Herrgott Oct. 20, 1908 1,441,594 Melcher Jan. 9, 1923 1,530,445 Warren Mar. 17, 1925 1,718,673 Wettstein June 25, 1929 1,790,620 -Davis Jan. 27, 1931 1,876,104 Tucker Sept. 6, 1932 1,972,852 Albright Sept. 11, 1934 r 2,016,824 Smith Oct. 8, 1935 2,106,036 OConner Jan. 18, 1938 2,117,891 Kalin May 17,1938 2,140,037 Swisher Dec. 13, 1938 2,160,779 Granat -May' 30, 1939 2,169,982 Manteuffel Aug. 15, 1939 2,188,834 Fischel Jan. 30, 1940 2,189,823 Vickers et al. Feb. 13, 1940 2,191,792 Hill Feb. 27, 1940 2,207,373 Dillworth July 9, 1940 2,291,011 Vickers July 28, 1942 2,333,184 Kalin Nov. 2, 1943 2,377,300 Pray May 29, .1945 2,398,421 Frische Apr. 16, 1946 FOREIGN PATENTS Number Country Date France May 8, 1933 9 (Addition to No. 42,494) 

